branchtargetfinder.java

ProGuard 是一个免费的 Java类文件的压缩

/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2007 Eric Lafortune ([e-mail])
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.optimize.peephole;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.*;
import proguard.classfile.constant.*;
import proguard.classfile.constant.visitor.ConstantVisitor;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.SimplifiedVisitor;

/**
 * This AttributeVisitor finds all instruction offsets, branch targets, and
 * exception targets in the CodeAttribute objects that it visits.
 *
 * @author Eric Lafortune
 */
public class BranchTargetFinder
extends      SimplifiedVisitor
implements   AttributeVisitor,
             InstructionVisitor,
             ExceptionInfoVisitor,
             ConstantVisitor
{
    public static final int NONE            = -2;
    public static final int AT_METHOD_ENTRY = -1;

    private static final short INSTRUCTION           = 1 <<  0;
    private static final short BRANCH_ORIGIN         = 1 <<  1;
    private static final short BRANCH_TARGET         = 1 <<  2;
    private static final short AFTER_BRANCH          = 1 <<  3;
    private static final short EXCEPTION_START       = 1 <<  4;
    private static final short EXCEPTION_END         = 1 <<  5;
    private static final short EXCEPTION_HANDLER     = 1 <<  6;
    private static final short SUBROUTINE_INVOCATION = 1 <<  7;
    private static final short SUBROUTINE_START      = 1 <<  8;
    private static final short SUBROUTINE            = 1 <<  9;
    private static final short SUBROUTINE_RETURNING  = 1 << 10;
    private static final short UNREACHABLE           = 1 << 11;

    private static final int MAXIMUM_CREATION_OFFSETS = 32;


    private short[] instructionMarks      = new short[ClassConstants.TYPICAL_CODE_LENGTH + 1];
    private int[]   subroutineStarts      = new int[ClassConstants.TYPICAL_CODE_LENGTH];
    private int[]   subroutineEnds        = new int[ClassConstants.TYPICAL_CODE_LENGTH];
    private int[]   creationOffsets       = new int[ClassConstants.TYPICAL_CODE_LENGTH];
    private int[]   initializationOffsets = new int[ClassConstants.TYPICAL_CODE_LENGTH];
    private int     superInitializationOffset;

    private int     minimumSubroutineEnd;
    private int[]   recentCreationOffsets = new int[MAXIMUM_CREATION_OFFSETS];
    private int     recentCreationOffsetIndex;
    private boolean isInitializer;


    /**
     * Returns whether there is an instruction at the given offset in the
     * CodeAttribute that was visited most recently.
     */
    public boolean isInstruction(int offset)
    {
        return (instructionMarks[offset] & INSTRUCTION) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is the target of
     * any kind in the CodeAttribute that was visited most recently.
     */
    public boolean isTarget(int offset)
    {
        return offset == 0 ||
               (instructionMarks[offset] & (BRANCH_TARGET   |
                                            EXCEPTION_START |
                                            EXCEPTION_END   |
                                            EXCEPTION_HANDLER)) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is the origin of a
     * branch instruction in the CodeAttribute that was visited most recently.
     */
    public boolean isBranchOrigin(int offset)
    {
        return (instructionMarks[offset] & BRANCH_ORIGIN) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is the target of a
     * branch instruction in the CodeAttribute that was visited most recently.
     */
    public boolean isBranchTarget(int offset)
    {
        return (instructionMarks[offset] & BRANCH_TARGET) != 0;
    }


    /**
     * Returns whether the instruction at the given offset comes right after a
     * definite branch instruction in the CodeAttribute that was visited most
     * recently.
     */
    public boolean isAfterBranch(int offset)
    {
        return (instructionMarks[offset] & AFTER_BRANCH) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is the start of an
     * exception try block in the CodeAttribute that was visited most recently.
     */
    public boolean isExceptionStart(int offset)
    {
        return (instructionMarks[offset] & EXCEPTION_START) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is the end of an
     * exception try block in the CodeAttribute that was visited most recently.
     */
    public boolean isExceptionEnd(int offset)
    {
        return (instructionMarks[offset] & EXCEPTION_END) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is the start of an
     * exception catch block in the CodeAttribute that was visited most recently.
     */
    public boolean isExceptionHandler(int offset)
    {
        return (instructionMarks[offset] & EXCEPTION_HANDLER) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is a subroutine
     * invocation in the CodeAttribute that was visited most recently.
     */
    public boolean isSubroutineInvocation(int offset)
    {
        return (instructionMarks[offset] & SUBROUTINE_INVOCATION) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is the start of a
     * subroutine in the CodeAttribute that was visited most recently.
     */
    public boolean isSubroutineStart(int offset)
    {
        return (instructionMarks[offset] & SUBROUTINE_START) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is part of a
     * subroutine in the CodeAttribute that was visited most recently.
     */
    public boolean isSubroutine(int offset)
    {
        return (instructionMarks[offset] & SUBROUTINE) != 0;
    }


    /**
     * Returns whether the subroutine at the given offset is ever returning
     * by means of a regular 'ret' instruction.
     */
    public boolean isSubroutineReturning(int offset)
    {
        return (instructionMarks[offset] & SUBROUTINE_RETURNING) != 0;
    }


    /**
     * Returns the start offset of the subroutine at the given offset, in the
     * CodeAttribute that was visited most recently.
     */
    public int subroutineStart(int offset)
    {
        return subroutineStarts[offset];
    }


    /**
     * Returns the offset after the subroutine at the given offset, in the
     * CodeAttribute that was visited most recently.
     */
    public int subroutineEnd(int offset)
    {
        return subroutineEnds[offset];
    }


    /**
     * Returns whether the instruction at the given offset is unreachable in
     * the CodeAttribute that was visited most recently.
     */
    public boolean isUnreachable(int offset)
    {
        return (instructionMarks[offset] & UNREACHABLE) != 0;
    }


    /**
     * Returns whether the instruction at the given offset is a 'new'
     * instruction, in the CodeAttribute that was visited most recently.
     */
    public boolean isNew(int offset)
    {
        return initializationOffsets[offset] != NONE;
    }


    /**
     * Returns the instruction offset at which the object instance that is
     * created at the given 'new' instruction offset is initialized, or
     * <code>NONE</code> if it is not being created.
     */
    public int initializationOffset(int offset)
    {
        return initializationOffsets[offset];
    }


    /**
     * Returns whether the method is an instance initializer, in the
     * CodeAttribute that was visited most recently.
     */
    public boolean isInitializer()
    {
        return superInitializationOffset != NONE;
    }


    /**
     * Returns the instruction offset at which this initializer is calling
     * the "super" or "this" initializer method, or <code>NONE</code> if it is
     * not an initializer.
     */
    public int superInitializationOffset()
    {
        return superInitializationOffset;
    }


    /**
     * Returns whether the instruction at the given offset is the special
     * invocation of an instance initializer, in the CodeAttribute that was
     * visited most recently.
     */
    public boolean isInitializer(int offset)
    {
        return creationOffsets[offset] != NONE;
    }


    /**
     * Returns the offset of the 'new' instruction that corresponds to the
     * invocation of the instance initializer at the given offset, or
     * <code>AT_METHOD_ENTRY</code> if the invocation is calling the "super" or
     * "this" initializer method, , or <code>NONE</code> if it is not a 'new'
     * instruction.
     */
    public int creationOffset(int offset)
    {
        return creationOffsets[offset];
    }


    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}


    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
    {
        // Make sure there are sufficiently large arrays.
        int codeLength = codeAttribute.u4codeLength;
        if (subroutineStarts.length < codeLength)
        {
            // Create new arrays.
            instructionMarks      = new short[codeLength + 1];
            subroutineStarts      = new int[codeLength];
            subroutineEnds        = new int[codeLength];
            creationOffsets       = new int[codeLength];
            initializationOffsets = new int[codeLength];

            // Reset the arrays.
            for (int index = 0; index < codeLength; index++)
            {
                creationOffsets[index]       = NONE;
                initializationOffsets[index] = NONE;
            }
        }
        else
        {
            // Reset the arrays.
            for (int index = 0; index < codeLength; index++)
            {
                instructionMarks[index]      = 0;
                subroutineStarts[index]      = 0;
                subroutineEnds[index]        = 0;
                creationOffsets[index]       = NONE;
                initializationOffsets[index] = NONE;
            }

            instructionMarks[codeLength] = 0;
        }

        superInitializationOffset = NONE;

        // We're not starting in a subroutine.
        minimumSubroutineEnd = Integer.MAX_VALUE;

        recentCreationOffsetIndex = 0;

        // Initialize the stack of 'new' instruction offsets if this method is
        // an instance initializer.
        if (method.getName(clazz).equals(ClassConstants.INTERNAL_METHOD_NAME_INIT))
        {
            recentCreationOffsets[recentCreationOffsetIndex++] = AT_METHOD_ENTRY;
        }

        // The end of the code is a branch target sentinel.
        instructionMarks[codeLength] = BRANCH_TARGET;

        // Mark branch targets by going over all instructions.